Background: Fibroblast growth factor 1 (FGF1) can regulate glucose and lipid metabolism in obese mice. Serum FGF1 has increased in type 2 diabetes mellitus adults and correlated with BMI. This study aimed to indicate conventional weight loss effects on FGF1 in obese children and adolescents. Materials and methods: Clinical and metabolic parameters of 88 lean and obese individuals (ages 5-15 years) and 39 obese individuals followed with 6 months of lifestyle intervention were collected. Serum FGF1 levels were detected through enzyme-linked immunosorbent assays. Results: FGF1 levels were increased in obese individuals. Serum FGF1 levels were significantly correlated with BMI and waist circumferences (r=0.377, P=0.012; r= 0.301, P=0.047, respectively). Multivariate stepwise linear regression analyses showed that FGF1 levels were significantly correlated with HbA1c and HOMA-IR (beta = 0.371, P=0.008; beta =0.323, P=0.021, respectively). Weight loss (2.3 +/- 0.1 kg) was accompanied by a significant reduction of circulating FGF1 levels (7.2 +/- 0.4 pg/mL). Changes in FGF1 were significantly correlated with changes in fasting glucose, HOMA-IR and low-density lipoprotein cholesterol (beta = 0.277, P=0.020; beta=0.474, P< 0.001; beta =0.320, P=0.008, respectively). Conclusion: FGF1 was related to increased risk of insulin resistance in obese children and adolescents. Serum FGF1 reduced after weight loss in obese individuals and was associated with the improvement of insulin resistance. Changes in serum FGF1 were more correlated with insulin resistance than changes in obesity per se.